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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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818                                ALASKAN GLACIER STUDIES
plotted in PL XCI and our contour maps. The depths shown were all obtained in 1910 except the one of 264 feet west of Haenke Island, which was made by the Corwin in 1890, two of 680 and 1002 feet respectively in the mouth of outer Yakutat Bay, made by the Coast Survey in 1892, and two of 720 feet (no bottom), south of Haenke Island, made by Malaspina in 1791. None of these soundings in 1910 are corrected for mean sea level and they were taken at various and unrecorded stages of tide. As the extreme range of tides at Yakutat village is seven to ten feet, and the maximum in Russell Fiord probably not greatly in excess of this, the greatest error in any sounding is surely less than ten feet, which for the purposes of this discussion is negligible. Not quite all our soundings are shown on PI. XCI, because of the small size of the map. Each sounding is plotted so that the middle of the figure is at the location of the sounding.
These soundings show specifically, what we had previously inferred, that the fiord is very deep. It reaches a maximum of 1119 feet below sea level in southern Russell Fiord, where it exceeds even the greatest recorded depth in outer Yakutat Bay. The depths in Disenchantment Bay range from 150 to 942 feet, with possibly greater depths in the western half of the bay, where the ice jam made sounding impossible. There is a channel east of Haenke Island sloping regularly southward from 264 to 576 feet. Northwestern Russell Fiord slopes southeastward from 216 to 888 feet, being shallowest, as Disenchantment Bay is also, near Hubbard and Variegated Glaciers. Nunatak Fiord has depths of from 261 to 666 feet, not sloping regularly as northwestern Russell Fiord does. Southern Russell Fiord has depths of from 786 to 1119 feet, with rapidly shoaling water in Seal Bay near Hidden Glacier and at the head of the bay where the fiord emerges from its mountain walls and- expands in the Yakutat Foreland. In all parts of the inlet the water, of course, shallows rapidly near shore but, as Russell observed, the fiord is everywhere deep and steep-sided.
The great depth below sea level, the form of the submerged topography, and the departures from normal slopes, etc., are all explained satisfactorily by glacial erosion, which seems to have completely erased the structural or stream-carved-and-submerged pre-glacial topography. The features in connection with glacial deposits below sea level will be taken up on a subsequent page. Those due to glacial sculpture fall under the headings of (a) the fiord cross-section, (b) the longitudinal bottom profile of fiords, (c) the submerged hanging valleys.
The fiord cross-section (Figs. 17 and 18) is plainly that of a round-bottomed V, as Davis has phrased it, rather than the often-quoted U-shape. The slopes above and below sea level are not essentially different. Knowing the depths of water in the fiord, and the steep-sided character of the fiords, the bulk of rock eroded in the formation of these fiords could be computed and the result would be a striking figure. How rapidly the water deepens offshore in places is shown by the fact that a sounding 100 yards from the coast near Pt. Latouche at the east entrance to Disenchantment Bay gave 312 feet, a slope of over 45 degrees. The fiord cross-section is a simple one and its large pattern is that of glacial erosion, in contrast with the angular pattern of faulting or the complex, small-textured pattern of stream erosion.
The longitudinal bottom profile of fiords, brings out three points: (1) we cannot distinguish irregularities due to glacial erosion from those due to glacial deposition below water by soundings alone; (2) the vertical range in the bottom profile constitutes a marked contrast between fiord-bottom profiles and those of stream valleys; (3) because of the